Both energy harvesting and storage are similarly constrained by materials availability and economics. Herein, we explore the dual use of earth-abundant and low cost Cu2ZnSnS4 (CZTS) inks not only for solar cells but also energy storage devices. In this report, we only focus on less addressed but important novel issues. One is the effect of CZTS layer thickness on solar cell performance. The other is the properties of CZTS as a supercapacitor electrode. For solar cells, a study of the effect of CZTS thickness on device performance of 55 solar cells revealed that the highest efficiencies are achieved at a CZTS thickness of approximately 0.37 mu m. For energy storage, we achieved a highest reported areal (and specific) capacitance of 2.67 F/cm(2) (1709 F/g) for CZTS. The dual use of CZTS for both energy harvesting and storage opens opportunities such as cheaper devices arising from economics of scale accompanying increased CZTS inks production.